Nanomaterials luminescence

Chiral nematic mesoporous films of Eu " doped Zr02 have been produced via a hard-templating approach using nanoctystalline cellulose-templated silica (Fig. 11). It was found that these chiral nematic nanostructures are capable of modulating the spontaneous emission of the Eu ions. The emission lines of the Eu " at 596 nm, 613 and 625 nm were significantly suppressed, and an increase in the luminescence lifetime is observed. It was suggested that these new chiral luminescent nanomaterials could find potential applications in sensing and new optical nanodevices. 

Luminescence of Lanthanide Ions in Coordination Compounds and Nanomaterials... 

The most prominent nanomaterials for bioanalysis at present are semiconductor QDs. Rare-earth doped upconverting nanocrystals and precious metal nanoparticles are becoming increasingly popular, yet they are still far from reaching the level of use of QDs. Other luminescent nanoparticles like carbon-based nanoparticles start to appear, but the synthesis and application of these materials are still in their infancy and not significant for practitioners in the field of bioanalysis. 

The photoluminescence of these nanoparticles has very different causes, depending on the type of nanomaterial semiconductor QDs luminescence by recombination of excitons, rare-earth doped nanoparticles photoluminescence by atom orbital (AO) transitions within the rare-earth ions acting as luminescent centers, and metallic nanoparticles emit light by various mechanisms. Consequently, the optical properties of luminescent nanoparticles can be very different, depending on the material they consist of. 

Why the absorption and luminescence spectra of Si02 and Ge02 nanomaterials can be drastically different from one another both in terms of maximum wavelength and band shape What is the origin of large Stokes shifts in these materials ... 

The advances in nanotechnology and synthesis methods have enabled nanomaterials to be produced in various shapes and structures. Coating of a luminescent layer activated by lanthanide ions on nanoparticles such as SiC>2 or AI2O3 is one of such approaches to develop new nanophosphors. In section 6, we review recent work on interesting spectroscopic features and luminescence dynamics of lanthanide ions in other novel low-dimensional nanostructures including core-shell, one-dimensional (ID) nanowires and nanotubes, two-dimensional (2D) nanofilms, hollow nanospheres, 2D nanosheet and nanodisk which have also attracted extensive attention. 

In addition to nanophenomena induced by confinement of the phonon density of states, luminescence decay time and efficiency of lanthanide ions in nanomaterials are also influenced... 

One of the chapters of this handbook has already made an in-depth discussion on luminescence of rare earth doped nanomaterials, presented by Liu and Chen (2007b). So in this chapter, we will focus on the chemical synthesis technology of inorganic rare earth nanomaterials, especially on the versatile solution-based routes, and recent discoveries and milestones in the synthesis and properties studies are systemically reviewed. The general physical synthesis routes, such as MOCVD, PLD, magnetron sputtering, would not be specifically mentioned in our chapter. 

Luminescence Photoluminescence of rare earth oxide nanocrystals is one of their most significant properties of interest for applications. The photoluminescence features of rare earth doped nanomaterials have been reviewed by Liu and Chen in an earlier chapter (Liu and Chen, 2007b). Therefore, we only review some related aspects, such as the major variations in the luminescence features of nanophased rare earth oxides, the application of rare earth doped nanocrystals as multicolor phosphors and as bioimaging probes. 

In addition to the orthophosphates, there are also a small number of reports on nanomaterials of other rare earth phosphate salts (Tang et al., 2005c). In this section, we will discuss the chemical synthesis of rare earth orthophosphates in aqueous solutions, nonaqueous solutions, and dry methods, together with the brief discussion of the luminescent properties, as well as the applications in biosensing. 

With this understanding, the spectra of Eu could probe the microstructure of nanomaterials, because the Dq to Fi transition was very sensitive to the site symmetry. Yan et al. used laser selective excitation technique to research the high-resolution spectra of f-YV04 Eu NPs (Yan et al., 2003a). When the Eu dopants approach the NPs surface, the D2d symmetry is broken. In emission spectra this is reflected by several points the increased number of emission lines the shortened luminescent lifetime, the enhanced splitting of energy levels, and the broadened emission peaks. 

Due to the high specificity and sensitivity of immunoassays, there are bioanalytical methods for the measurement of an analyte of interest, with little or without preconcentration or purification of the samples. The principle behind immunoassays is based on an interaction between an antibody and a corresponding antigen, and the detection of the specific interaction using radiolabels (247), enzyme, fluorescent and luminescent compounds (178, 179,181,183), electroactive markers (177,180, 228, 248), or nanomaterials (249-251). 

An attractive alternative to organic fluorophores in formulated polymeric sensor films for chemical detection is to use inorganic luminescent materials. Semiconductor nanocrystals have a dramatically improved photostability and are attractive as luminescent labels.1415 However, some nanocrystals also exhibit photoluminescence (PL) that is sensitive to the local environment. For example, it was observed that PL of CdSe nanocrystals incorporated into polymer thin films responded reversibly to different gases.16 Because in sensing applications nanomaterials bring previously unavailable capabilities1719 and unexpected results,20 23 we explored the environmental sensitivity of semiconductor nanocrystals upon their incorporation in different rationally selected polymeric matrices.24 26... 

The luminescence properties of nanoscale diamond have as well been subject to extensive study. For nanoscopic particles, as compared to the respective bulk material, deviating characteristics are generally expected due to the large portion of surface atoms and a potentially distorted band structure. Yet for diamond, the bandgap is unaffected by particle dimensions (at least in the relevant range), and the luminescence of the nanomaterial has many features in common with that of the bulk phase. 

Even larger probes of bent and kinked DNA are 40 A photoluminescent mineral colloidal particles of CdS [247-253]. These nanoparticles are approximately the size of proteins and can be made in a variety of sizes ( 20-100 A) and decorated with a variety of surface groups [267-279]. The emission spectrum of a nanoparticle solution depends on particle size and surface group synthetic procedures for CdS and other semiconductor nanoparticles have been developed so that the emission can be tuned throughout the visible spectrum and into the near infrared [267-279]. Moreover, the photoluminescence of CdS is sensitive to adsorbates [280-289], and thus these nanomaterials can function as luminescent chemical sensors. 

Optoelectronic nanodevices that rely on electric field effects in optical absorption and emission provide the ability to be controlled conveniendy using integrated electronic platforms. Semiconductor quantum dots are theoretically expected as an excellent candidate for such optoelectronic nanomaterials to show optical properties strongly dependent on electric field [1]. In the general class of quantum dots, chemically synthesized semiconductor nanocrystals also exhibit electric field effects, for example, as demonstrated in their optical absorption (e.g. the quantum confined Stark effect [2,3]) and in their optical emission as the Stark shift and luminescence quenching [4,5]). 

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